Lithium composite metal oxide, positive electrode active substance, positive electrode, and non-aqueous electrolyte secondary battery

ABSTRACT

A lithium composite metal oxide that contains Li, Ni, and Mn, has a layered structure, has a diffraction peak in a range of 2θ=20.8±1° in a powder X-ray diffraction pattern obtained with powder X-ray diffraction measurement using a Cu-Kα radiation, has a BET specific surface area in a range of 6 m 2 /g to 30 m 2 /g, and has an average particle diameter measured with a laser diffraction scattering method in a range of 0.1 μm to 10 μm.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is Continuation of U.S. application Ser. No. 14/408,487filed Dec. 16, 2014 which is a National Stage Entry of InternationalApplication No. PCT/JP2013/068452 filed Jun. 28, 2013, claiming benefitto Japanese Patent Application No. 2012-153048 filed Jul. 6, 2012, thecontents of each of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a lithium composite metal oxide, apositive electrode active material, a positive electrode, and anon-aqueous electrolyte secondary battery.

BACKGROUND ART

A lithium composite metal oxide is used as a positive electrode activematerial in a non-aqueous electrolyte secondary battery such as alithium secondary battery. The lithium secondary battery has alreadybeen put into practical use as a small size power supply for mobilephones, notebook computers, etc., and furthermore, there has been anattempt to utilize the lithium secondary battery as a medium or largesize power supply for automobiles, power storage, etc.

Recently, with downsizing and multifunctioning portable devices, therehas been an increasing demand for a non-aqueous electrolyte secondarybattery having a high energy density, and the development of anon-aqueous electrolyte secondary batteries in excellent characteristicsis more desired than ever.

As an existing lithium composite metal oxide, Patent literature 1concretely discloses a lithium composite metal oxide which has acomposition of Li:Mn:Ni:Co=1.06:0.43:0.34:0.16 and a BET specificsurface area of 1.16 m²/g, and which exhibits a discharge capacity of197.4 mAh/g when it is used as a positive electrode active material fora lithium secondary battery.

REFERENCE LIST Patent Literature

[Patent Literature 1] Japanese Patent Application Publication No.2009-245955

SUMMARY OF INVENTION

A non-aqueous electrolyte secondary battery obtained with using theexisting lithium composite metal oxide as described above as a positiveelectrode active material, however, is not sufficient one for the use inwhich a high discharge capacity is required, for example, a small sizepower supply used in a downsizing and multifunctioning portable device.

In addition, while the existing non-aqueous electrolyte secondarybattery is designed to be driven with an upper limit voltage ofapproximately 4.3 V relative to lithium as the reference, in recentyears, there has been an attempt to increase the capacity of thenon-aqueous electrolyte secondary battery by driving a battery with ahigher voltage than usual, that is, an upper limit voltage ofapproximately 4.6 V to 4.8 V relative to lithium as the reference.Therefore, there has been a demand for a positive electrode activematerial for a non-aqueous electrolyte secondary battery capable ofbeing driven with such a higher voltage.

Furthermore, as an index for evaluating the performance of a secondarybattery, the initial coulomb efficiency is known. The “initial coulombefficiency” refers to a value obtained from (initial dischargecapacity)/(initial charge capacity)×100 (%). Since a secondary batteryhaving a high initial coulomb efficiency has a small irreversiblecapacity at the time of initial charge and discharge, and tends to havea greater capacity per volume and weight, a secondary battery exhibitingas high an initial coulomb efficiency as possible is desired.

The present invention has been made in consideration of theabove-described circumstances, and an object of the present invention isto provide a lithium composite metal oxide used in a non-aqueouselectrolyte secondary battery capable of increasing the dischargecapacity and the initial coulomb efficiency at a higher upper limitvoltage than usual. In addition, another object is to provide a positiveelectrode active material, a positive electrode, and a non-aqueouselectrolyte secondary battery for which the above-described lithiumcomposite metal oxide is used.

In order to solve the above-described problems, an aspect of the presentinvention provides a lithium composite metal oxide which contains Li,Ni, and Mn, has a layered structure, has a diffraction peak in a rangeof 2θ=20.8±1° in a powder X-ray diffraction pattern obtained with powderX-ray diffraction measurement using a Cu-Kα radiation, has a BETspecific surface area in a range of 6 m²/g to 30 m²/g, and has anaverage particle diameter measured with a laser diffraction scatteringmethod in a range of 0.1 μm to 10 μm.

In other aspect of the present invention, an average primary particlediameter of the lithium composite metal oxide is preferably in a rangeof 0.05 μm to 0.3 μm.

In other aspect of the present invention, the lithium composite metaloxide is preferably expressed by Formula (A) described below

Li_(a)Ni_(1-x-y)Mn_(x)M_(y)O₂   (A)

(Here, 1.1≦a≦1.6, 0.4≦x≦0.8, 0≦y≦0.25, 0.5≦x+y≦0.8, and M represents oneor more elements selected from the group consisting of Co, Fe, Mg, Al,and Ca).

In other aspect of the present invention, the lithium composite metaloxide is preferably expressed by Formula (B) described below

nLi_(2b/3)MnO₃·(1-n) Li_(b/3)Ni_(1-p-q)Mn_(p)M_(q)O₂   (B)

(Here, 0.2≦n≦0.6, 2.75≦b<3.0, 0.25≦p≦0.5, 0≦q≦0.31, 0.38≦p+q≦0.5, and Mrepresents one or more elements selected from the group consisting ofCo, Fe, Mg, Al, and Ca).

In other aspect of the present invention, the M in Formulae (A) and (B)are preferably either one of or both of Co and Fe.

In addition, other aspect of the present invention is a positiveelectrode active material comprising the lithium composite metal oxide.

In addition, other aspect of the present invention is a positiveelectrode comprising the positive electrode active material.

In addition, other aspect of the present invention is a non-aqueouselectrolyte secondary battery comprising a negative electrode and thepositive electrode.

In the aspect of the present invention, a charge potential of thepositive electrode in a fully charged state is preferably 4.35 V (vs.Li/Li⁺) or more.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) and FIG. 1(b) are schematic views illustrating an example of anon-aqueous electrolyte secondary battery of the present embodiment.

REFERENCE SIGNS LIST

1 . . . SEPARATOR, 2 . . . POSITIVE ELECTRODE, 3 . . . NEGATIVEELECTRODE, 4 . . . ELECTRODE GROUP, 5 . . . BATTERY CAN, 6 . . .ELECTROLYTE SOLUTION, 7 . . . TOP INSULATOR, 8 . . . SEALING BODY, 10 .. . NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY, 21 . . . POSITIVEELECTRODE LEAD, 31 . . . NEGATIVE ELECTRODE LEAD

Description of Embodiments

[Lithium Composite Metal Oxide]

A lithium composite metal oxide of the present embodiment contains Li,Ni, and Mn, has a layered structure, has a diffraction peak in a rangeof 2θ=20.8±1° in a powder X-ray diffraction pattern obtained with powderX-ray diffraction measurement using a Cu-Kα radiation, has a BETspecific surface area in a range of 6 m²/g to 30 m²/g, and has anaverage particle diameter measured with a laser diffraction scatteringmethod in a range of 0.1 μm to 10 μm.

Hereinafter, what has been described above will besequentiallydescribed.

(Layered Structure)

The crystal structure of the lithium composite metal oxide of thepresent embodiment is a layered structure, and is more preferably ahexagonal crystal structure or a monoclinic crystal structure.

The hexagonal crystal structure belongs to any one of the space groupselected from the group consisting of P3, P3₁, P3₂, R3, P-3, R-3, P312,P321, P3₁12, P3₁21, P3₂12, P3₂21, R32, P3m1, P31m, P3c1, P31c, R3m, R3c,P-31m, P-31c, P-3m1, P-3c1, P-3m, R-3c, P6, P6₁, P6₅, P6₂, P6₄, P6₃,P-6, P6/m, P6₃/m, P622, P6₁22, P₅22, P6₂22, P6₄22, P6₃22, P6mm, P6cc,P6₃cm, P6₃mc, P-6m2, P-6c2, P-62m, P-62c, P6/mmm, P6/mcc, P6₃/mcm, andP6₃/mmc.

In addition, the monoclinic crystal structure belongs to any one of thespace group selected from the group consisting of P2, P2₁, C2, Pm, Pc,Cm, Cc, P2/m, P2₁/m, C2/m, P2/c, P2₁/c, and C2/c.

Among the above-described crystal structures, since the dischargecapacity of the obtained non-aqueous electrolyte secondary batteryincreases, the particularly preferable crystal structure of the lithiumcomposite metal oxide is a hexagonal crystal structure belonging to R-3mor a monoclinic crystal structure belonging to C2/m.

The space group of the lithium composite metal oxide of the presentembodiment can be confirmed using the following method.

First, powder X-ray diffraction measurement in which Cu-Kαπis used as aradiation source and the measurement range of a diffraction angle 2θ isset in a range of 10° to 90° is carried out on the lithium compositemetal oxide, subsequently, Rietveld analysis is carried out on the basisof the result (the obtained powder X-ray diffraction pattern), and thecrystal structure which the lithium composite metal oxide has and thespace group in the crystal structure are determined. The Rietveldanalysis is a method in which the crystal structure of a material isanalyzed using the data of diffraction peaks(diffraction peak intensityand diffraction angle 2θ) in the powder X-ray diffraction measurement ofthe material, and a method that has been conventionally used (forexample, refer to “Practice of powder X-ray analysis —Introduction tothe Rietveld method” published on Feb. 10, 2002, and edited byConference for X-ray analysis in The Japan Society for AnalyticalChemistry).

(Diffraction Peak in Powder X-Ray Diffraction Diagram)

The lithium composite metal oxide of the present embodiment has adiffraction peak in a range of 2θ=20.8±1°, that is, in a range of19.8≦2θ≦21.8° in the powder X-ray diffraction pattern obtained with thepowder X-ray diffraction measurement using a Cu-Kα radiation.

As described above, the crystal of the lithium composite metal oxide ofthe present embodiment has a layered structure. When the lithiumcomposite metal oxide having a layered structure is expressed as LiMO₂,individual layers can be schematically divided into (1) a layerconstituted of a Li ion, (2) a layer constituted of an oxygen (O) ion,and (3) a layer constituted of a metal (M) ion other than the Li ion(hereinafter, the layer of (3) may be, in some cases, referred to as“metal ion layer”). When a non-aqueous electrolyte secondary battery isconstituted using the above-described lithium composite metal oxide as apositive electrode active material, the Li ion in (1) the layerconstituted of the Li ion is mainly emitted from the crystal or absorbedin the crystal, and the non-aqueous electrolyte secondary battery ischarged and discharged.

Here, in the lithium composite metal oxide of the present embodiment,the diffraction peak appearing in the range of 2θ=20.8±1° in the powderX-ray diffraction pattern indicates that the crystal of the measuredlithium composite metal oxide has a long-distance order. Specifically,the diffraction peak indicates that a Li ion is present in (3) the metalion layer (the metal ion layer includes a Li ion), and theabove-described metal ion layer is periodically present over a longdistance, and therefore the diffraction peak appears in theabove-described range. In the lithium composite metal oxide having theabove-described structure, since the Li ion used for charging anddischarging is included not only in (1) the layer constituted of a Liion but also in (3) the metal ion layer, the capacity of the non-aqueouselectrolyte secondary battery is increased using the lithium compositemetal oxide as a positive electrode active material.

In the non-aqueous electrolyte secondary battery using the lithiumcomposite metal oxide of the present embodiment, in order to obtain ahigh discharge capacity, the diffraction peak in the range of 2θ=20.8±1°in the powder X-ray diffraction pattern obtained with the powder X-raydiffraction measurement using a Cu-Kα radiation has a value obtained bydividing the maximum intensity of the peak by the maximum intensity of adiffraction peak in a range of 2θ=18.6±1° (17.6≦°2θ≦19.6°), preferablyin a range of 0.03 to 20, and more preferably in a range of 0.05 to 10.

(BET Specific Surface Area)

The BET specific surface area of the lithium composite metal oxide ofthe present embodiment is in a range of 6 m²/g to 30 m²/g. When the BETspecific surface area is 6 m²/g or more, the discharge capacity of theobtained non-aqueous electrolyte secondary battery is favorable, and,when the BET specific surface area is 30 m²/g or less, the cyclecharacteristics (the capacity maintenance rate when the battery isrepeatedly charged and discharged) of the obtained non-aqueouselectrolyte secondary battery are favorable. Therefore, the lithiumcomposite metal oxide of the present embodiment become excellent in thedischarge capacity and cycle characteristics of the obtained non-aqueouselectrolyte secondary battery.

In order to further improve the effects of the present embodiment, theBET specific surface area of the lithium composite metal oxide ispreferably 7 m²/g or more, and more preferably 9 m²/g or more. Inaddition, in order to improve the filling properties, the BET specificsurface area of the lithium composite metal oxide is preferably 25 m²/gor less, and more preferably 20 m²/g or less. The above-described upperlimit value and lower limit value may be adequately combined together.

(Average Particle Diameter)

The average particle diameter of the lithium composite metal oxide ofthe present embodiment is in a range of 0.1 μm to 10 μm, and preferablyin a range of 0.1 μm to less than 10 μm. By this, it is possible toincrease the capacity maintenance rate (cycle characteristics) when thebattery is repeatedly charged and discharged and the discharge capacitymaintenance rate at a high current rate. The average particle diameterof the lithium composite metal oxide is more preferably in a range of0.2 μm to 5 μm, and still more preferably in a range of 0.3 μm to 1 μm.

In the present embodiment, the “average particle diameter” of thelithium composite metal oxide refers to a value measured by thefollowing method (a laser diffraction scattering method).

First, 0.1 g of lithium composite metal oxide powder is put into 50 mlof a 0.2 mass % sodium hexametaphosphate aqueous solution, and adispersion liquid in which the powder is dispersed is obtained. Theparticle size distribution of the obtained dispersion liquid is measuredusing a MASTERSIZER 2000 (a laser diffraction scattering particle sizedistribution measuring instrument) manufactured by Malvern InstrumentsLtd., and a volume-based cumulative particle size distribution curve isobtained. In the obtained cumulative particle size distribution curve,the value of the particle diameter (D₅₀) from the micro particle side atthe point of 50% accumulation is the average particle diameter of thelithium composite metal oxide.

(Other Characteristics)

In order that the lithium composite metal oxide of the presentembodiment obtains a high initial coulomb efficiency, the averageprimary particle diameter of the lithium composite metal oxide ispreferably in a range of 0.05 μm to 0.3 μm, and more preferably in arange of 0.07 μm to 0.25 μm.

In the present embodiment, the “average primary particle diameter” ofthe lithium composite metal oxide refers to a value measured by thefollowing method.

First, lithium composite metal oxide powder is placed on a conductivesheet attached onto a sample stage, and SEM observation is carried outby radiating an electron beam with an accelerated voltage of 20 kV usinga JSM-5510 manufactured by JEOL Ltd. 50 primary particles arearbitrarily selected in an image (SEM photograph) obtained from the SEMobservation, parallel lines are drawn from a certain direction so as tohold the projection image of each primary particle, and the distance(unidirectional particle diameter) between the parallel lines ismeasured as the particle diameter of the primary particle. Thearithmetic average value of the obtained particle diameters of theprimary particles is the average primary particle diameter of thelithium composite metal oxide.

In addition, the “average secondary particle diameter” of the secondaryparticles of the lithium composite metal oxide refers to the arithmeticaverage value of the particle diameters of secondary particles measuredby the same method as the above-described method for measuring theaverage primary particle diameter.

(Composition Formula of Lithium Composite Metal Oxide)

In order to obtain a non-aqueous electrolyte secondary battery having ahigher discharge capacity, the lithium composite metal oxide of thepresent embodiment is preferably expressed by Formula (A) describedbelow.

Li_(a)Ni_(1-x-y)Mn_(x)M_(y)O₂   (A)

(Here, 1.1≦a≦1.6, 0.4≦x≦0.8, 0≦y≦0.25, 0.5≦x+y≦0.8, and M represents oneor more elements selected from the group consisting of Co, Fe, Mg, Al,and Ca).

Alternatively, the lithium composite metal oxide of the presentembodiment is preferably expressed by Formula (B) described below.

nLi_(2b/3)MnO₃·(1n)Li_(b/3)Ni_(1-p-q)Mn_(p)M_(q)O₂   (B)

(Here, 0.2≦n≦0.6, 2.75≦b<3.0, 0.25≦p≦0.5, 0≦q≦0.31, 0.38≦p+q≦0.5, and Mrepresents one or more elements selected from the group consisting ofCo, Fe, Mg, Al, and Ca).

In Formulae (A) and (B), in order to increase the discharge capacity andobtain a non-aqueous electrolyte secondary battery having a high initialcoulomb efficiency, the molar ratio of Li/(Mn+Ni+M) is preferably in arange of 1.1 to 1.6, and more preferably in a range of 1.15 to 1.5.

In Formulae (A) and (B), in the case of a non-aqueous electrolytesecondary battery being obtained, to increase the capacity maintenancerate when the battery is repeatedly charged and discharged (cyclecharacteristics), the molar ratio of Mn/(Mn+Ni+M) is preferably in arange of 0.4 to 0.8, and more preferably in a range of 0.45 to 0.7.

In Formulae (A) and (B), in the case of a non-aqueous electrolytesecondary battery being obtained, to increase the discharge capacitymaintenance rate at a high discharge rate, the molar ratio ofNi/(Mn+Ni+M) is preferably in a range of 0.2 to 0.5, and more preferablyin a range of 0.25 to 0.45.

In Formulae (A) and (B), in the case of a non-aqueous electrolytesecondary battery being obtained, to increase the average dischargevoltage, the molar ratio of M/(Mn+Ni+M) is preferably in a range of 0 to0.25, and more preferably in a range of 0.03 to 0.20.

In Formulae (A) and (B), to increase the average discharge voltage, theM is preferably Co, Fe, Mg, Al, or Ca and particularly preferably Co orFe. The M may be singly used, or a mixture of two or more Ms may beused.

In Formula (B), to increase the discharge capacity in the case of anon-aqueous electrolyte secondary battery being obtained, n ispreferably 0.2 or more, and more preferably 0.25 or more. In addition,to obtain a non-aqueous electrolyte secondary battery having a highinitial coulomb efficiency, n is preferably 0.6 or less, and morepreferably 0.5 or less. The above-described upper limit value and lowerlimit value may be adequately combined together.

A positive electrode active material including the lithium compositemetal oxide of the present embodiment is preferable for a non-aqueouselectrolyte secondary battery.

(Method for Producing Lithium Composite Metal Oxide)

Next, the method for producing the lithium composite metal oxide will bedescribed.

The lithium composite metal oxide of the present embodiment has adiffraction peak in a range of 2θ=20.8±1° in a powder X-ray diffractionpattern obtained with powder X-ray diffraction measurement using a Cu-Kαradiation. In order to obtain the above-described lithium compositemetal oxide, at the time of production, it is preferable to use agreater amount of a material corresponding to Li than materialscorresponding to metals other than Li, and to increase the amount (molarratio) of Li with respect to the metals other than Li included in amixture before heating described below.

An example of the method for producing the lithium composite metal oxideof the present embodiment is a method including the following steps (1),(2), and (3) in this order.

(1) A step of obtaining a slurry by bringing an aqueous solution(hereinafter, in some cases, referred to as “raw material aqueoussolution”) including a Ni ion, a Mn ion, and an ion of a metalrepresented by M and alkali into contact with each other to generate aco-precipitate.

(2) A step of obtaining a co-precipitate from the slurry obtained in(1).

(3) A step of heating a mixture obtained by mixing the co-precipitateobtained in (2) and a lithium compound at a temperature in a range of650° C. to 950°.

(Step (1))

In the step (1), the raw material aqueous solution may be prepared bydissolving a compound containing Ni and a compound containing Mn inwater. The compound containing Ni and the compound containing Mn arepreferably water-soluble salts, and more preferably sulfates.

Similarly, a compound containing M (one or more elements selected fromthe group consisting of Co, Fe, Mg, Al, and Ca) that is used in forpreparing the raw material aqueous solution is preferably awater-soluble salt. Particularly, when M is either of or both of Fe andCo, a sulfate of M is preferably used, and a divalent sulfate is morepreferable.

The raw material aqueous solution is preferably an aqueous solutionobtained by dissolving a sulfate of Ni, a sulfate of Mn, and a sulfateof M in water.

When each raw material containing Ni, Mn, or M are not easily dissolvedin water, for example, when each raw material is an oxide, a hydroxide,and a metal material, it is possible to obtain the raw material aqueoussolution by dissolving these raw materials in an aqueous solutioncontaining sulfuric acid.

The raw material aqueous solution may be prepared by preparingseparately aqueous solutions for individual metals used, and then mixingall the aqueous solutions, or may be prepared by dissolving a compoundcontaining Ni, Mn, and M in a commonly used solvent (water or sulfuricacid).

The alkali used in the step (1) may be one or more salts selected fromthe group consisting of LiOH (lithium hydroxide), NaOH (sodiumhydroxide), KOH (potassium hydroxide), Li₂CO₃ (lithium carbonate),Na₂CO₃ (sodium carbonate), K₂CO₃ (potassium carbonate), and (NH₄)₂CO₃(ammonium carbonate). The alkali used may be an anhydride or a hydrate.An anhydride and a hydrate may be jointly used. In the step (1), anaqueous solution of the above-described alkali (alkali aqueous solution)is preferably used. As the alkali aqueous solution, it is also possibleto use ammonia water.

The concentration of the alkali in the alkali aqueous solution ispreferably in a range of approximately 0.5 M to 10 M (mol/L), and morepreferably in a range of approximately 1 M to 8 M. In addition, informthe viewpoint of the production costs, NaOH or KOH is preferably used asthe alkali. In addition, two or more alkalis described above may bejointly used.

Examples of the contact method in the step (1) include (i) a method inwhich the alkali aqueous solution is added to and mixed with the rawmaterial aqueous solution, (ii) a method in which the raw materialaqueous solution is added to and mixed with the alkali aqueous solution,and (iii) a method in which the raw material aqueous solution and thealkali aqueous solution are added to and mixed with water. During themixing, stirring is preferably carried out.

Among the contact methods in the step (1), (ii) the method in which theraw material aqueous solution is added to and mixed with the alkaliaqueous solution is preferable since it is easy to control the change inpH. In the case of this method, as the raw material aqueous solution isadded to and mixed with the alkali aqueous solution, the pH of thealkali aqueous solution tends to decrease, and it is preferable to addthe raw material aqueous solution with controlling the pH to be 9 ormore, and preferably to be 10 or more. In addition, when the aqueoussolutions are brought into contact with each other with maintaining atemperature of either or both of the raw material aqueous solution andthe alkali aqueous solution in a range of 40° C. to 80° C., aco-precipitate having a more homogeneous composition can be preferablyobtained.

In the step (1), by bringing the raw material aqueous solution and thealkali into contact with each other in the above-described manner, it ispossible to co-precipitate and generate a salt including a Ni ion, a Mnion, and an ion of a metal represented by M and to obtain a slurry inwhich the salt that is a co-precipitate is dispersed, .

(Step (2))

In the step (2), a co-precipitate is obtained from the slurry obtainedin the step (1). In the step (2), a variety of methods may be employedas a method for obtaining the co-precipitate as long as theco-precipitate can be obtained, and a method by a separation operationwhich produces a solid component such as filtration is preferable sincethe operation is simple. The co-precipitate may be obtained by a methodin which liquid is volatilized by heating such as the spraying anddrying of the slurry.

In the case of obtaining the co-precipitate in the step (2), it ispreferable to wash and dry the co-precipitate separated in the step (2).By washing the co-precipitate, it is possible to reduce the amount of analkali remaining in the obtained co-precipitate or a SO₄ ²⁻ ion beingliberated in the raw material aqueous solution in the case of using asulfate of Ni, a sulfate of Mn, and a sulfate of M as raw materials.When the amount thereof is reduced by washing, the control of the amountof an inert fusing agent (described below) becomes easy and that ispreferable.

In order to efficiently wash the co-precipitate, water is preferablyused as a washing liquid. A water-soluble organic solvent such as analcohol or acetone may be added to the washing liquid as necessary. Thewashing may be carried out twice or more, and, for example, it may bepossible to wash the co-precipitate using water, and then wash again theco-precipitate using the above-described water-soluble organic solvent.

The drying of the washed co-precipitate can be carried out by a thermaltreatment, and may also be carried out by blow drying, vacuum drying,etc., or a combination thereof. When the co-precipitate is dried by athermal treatment, the heating temperature is preferably in a range of50° C. to 300° C., and more preferably in a range of approximately 100°C. to 200° C.

A co-precipitate obtained by washing and drying the co-precipitatepreferably has a BET specific surface area in a range of approximately10 m²/g to 130 m²/g. The BET specific surface area of the co-precipitatecan be controlled using the drying temperature. When the dryingtemperature is set to be lower, a co-precipitate having a smaller BETspecific surface area is obtained, and, when the drying temperature isset to be higher, a co-precipitate having a larger BET specific surfacearea is obtained.

In order to accelerate the reactivity during heating described below,the BET specific surface area of the co-precipitate is preferably 20m²/g or more, and more preferably 30 m²/g or more. In addition, sincethe co-precipitate is easy to handle, the BET specific surface area ofthe co-precipitate is preferably 100 m²/g or less, and more preferably90 m²/g or less. The upper limit value and lower limit value of the BETspecific surface area may be adequately combined together.

The co-precipitate obtained in the step (2) is preferably constituted amixture of primary particles having an average particle diameter(average primary particle diameter) of from 0.001 μm to 0.1 μm andsecondary particles formed by the agglomeration of the primary particleshaving an average secondary particle diameter (average secondaryparticle diameter) of from 1 μm to 100 μm. The method for measuring theaverage primary particle diameter is as described above. The averagesecondary particle diameter can also be obtained in accordance with themethod for measuring the average primary particle diameter. The averagesecondary particle diameter of the secondary particles is preferablyfrom 1 μm to 50 μm, and more preferably from 1 μm to 30 μm.

(Step (3))

In the step (3), the co-precipitate obtained in the step (2) and alithium compound are mixed together to produce a mixture, and theobtained mixture is heated.

Examples of the lithium compound include one or more salts selected fromthe group consisting of lithium hydroxide, lithium chloride, lithiumnitrate, and lithium carbonate. The lithium compound being used may bean anhydride or a hydrate. An anhydride and a hydrate may be jointlyused.

In order to obtain a non-aqueous electrolyte secondary battery having ahigher discharge capacity, in the mixture obtained by mixing theco-precipitate obtained in the step (2) and a lithium compound, theamount (mole) of Li with respect to the total amount (mole) of Ni, Mn,and M (M represents one or more elements selected from the groupconsisting of Co, Fe, Mg, Al, and Ca) (Li/(Ni+Mn+M)) is preferably from1.1 to 1.6, and more preferably from of 1.3 to 1.5.

The mixing may be carried out by any of dry mixing and wet mixing, anddry mixing is preferable since the operation is simple. Examples of themixing apparatus include agitation mixer, a V-shaped mixer, a W-shapedmixer, a ribbon mixer, a drum mixer, a ball mill, etc.

The heating temperature during the heating in the step (3) is animportant factor to control the BET specific surface area of the lithiumcomposite metal oxide. The BET specific surface area of the obtainedlithium composite metal oxide tends to decrease with the increase of theheating temperature during the heating.

For example, when the compositional ratio (molar ratio) between Ni andMn in the co-precipitate obtained in the step (2) is 1:1, in the step(3), the BET specific surface area of the lithium composite metal oxideobtained with calcining at a heating temperature of 1000° C. is as smallas 0.3 m²/g, and the discharge capacity maintenance rate at a highcurrent rate does not result in sufficient. As the heating temperaturedecreases to lower than the above-described heating temperature, the BETspecific surface area tends to increase. In order to obtain the BETspecific surface area of the lithium composite metal oxide of from 6m²/g to 30 m²/g, the heating temperature is preferably from 650° C. to950° C. The heating temperature may be maintained at a fixed temperatureduring heating, and, when the heating temperature is within theabove-described heating temperature range, the temperature condition maybe changed during the heating.

The time for keeping the above-described heating temperature ispreferably from 0.1 hours to 20 hours, and more preferably from 0.5hours to 8 hours.

The rate of temperature increase up to the above-described heatingtemperature is preferably from 50° C./hour to 400° C/hour. In addition,the rate of temperature decrease from the above-described heatingtemperature to room temperature is preferably from 10° C./hour to 400°C./hour.

As the atmosphere for the heating in the step (3), it is possible to usean air, oxygen, nitrogen, argon, or a gas mixture thereof, and an air ispreferable.

The lithium composite metal oxide of the present embodiment can beproduced by the above-described steps (1) to (3).

The production method of the present embodiment has been described toinclude the steps from (1) to (3), but is not limited thereto. Forexample, it is possible to produce the lithium composite metal oxide ofthe present embodiment by preparing a mixture obtained by mixing a saltincluding a Ni ion, a Mn ion, and an M ion and the lithium compoundusing a other method replacing a part of the steps (1), (2), and (3),and heating the obtained mixture under the conditions of the step (3).

The above-described “salt including a Ni ion, a Mn ion, and an M ion”may be a mixture of a salt including a Ni ion, a salt including a Mnion, and a salt including an M ion. Examples of the above-described “aother method replacing a part of the steps (1), (2), and (3)” include amethod for mixing the above-described salt in a solid phase, a method inwhich the above-described salt is dispersed in a liquid phase to producea slurry and the obtained slurry is sprayed, dried, and mixed, etc.

(Inert Fusing Agent)

At the time of the heating in the step (3), the mixture may include aninert fusing agent such as ammonium fluoride or boric acid. The inertfusing agent is also called a flux or a fusing agent, and is a salt thatdoes not react with a composite metal oxide which is a target substance,and is easily separated from the target substance. The inert fusingagent is fused at the heating temperature in the step (3), forms areaction field, and accelerates a uniform reaction. Therefore, when theinert fusing agent is used, a product having a homogeneous compositionis easily obtained.

More specific examples of the inert fusing agent include sulfates suchas K₂SO₄ and Na₂SO₄; carbonates such as K₂CO₃ and Na₂CO₃; chlorides suchas NaCl, KCl, and NH₄Cl; fluorides such as LiF, NaF, KF, and HN₄F; andboric acid. Among the above-described inert fusing agents, sulfates arepreferable, and K₂SO₄ is more preferable. Two or more inert fusingagents may also be jointly used.

When the mixture includes the inert fusing agent, the reactivity of themixture during the heating improves, and therefore the BET specificsurface area of the obtained lithium composite metal oxide can becontrolled. In the case of the heating temperatures being the same, asthe content of the inert fusing agent in the mixture increases, the BETspecific surface area of the oxide tends to increase. In addition,during the heating, when the inert fusing agent is included, a uniformreaction can be carried out, and therefore the local structure of thelithium composite metal oxide can be controlled at an atomic level bycontrolling the heating atmosphere.

The inert fusing agent can be added and mixed in when the co-precipitateand the lithium compound are mixed together in the step (3). Inaddition, the inert fusing agent may remain in the lithium compositemetal oxide, or may be removed by washing.

The inert fusing agent may be mixed with the obtained co-precipitate byadding a solution of the inert fusing agent to the co-precipitateobtained by the separation operation in the step (2), and drying themixture.

For example, in the step (1), when a sulfate of Ni, a sulfate of Mn, ora sulfate of M is used as a raw material, a SO₄ ²⁻ ion is liberated inthe raw material aqueous solution. The SO₄ ²⁻ ion and a metal ionincluded in the alkali used for the co-precipitation (for example, inthe case of using KOH as the alkali, a metal ion is a K ion)occasionally remain in the co-precipitate separated in the step (2), andthe inert fusing agent (K₂SO₄ in the above-described example) isgenerated. Therefore, the inert fusing agent may be mixed with theobtained co-precipitate by using the raw material aqueous solution afterthe co-precipitation in the step (1) as the above-described “solution ofthe inert fusing agent”, and drying the co-precipitate obtained in thestep (2) to which the raw material aqueous solution after theco-precipitation has been added.

The inert fusing agent may be added and mixed in when the co-precipitateand the lithium compound are mixed with each other in the step (3).Since the amount of the inert fusing agent is easily controlled, themethod in which the inert fusing agent is added in the step (3) is morepreferable than the above-described method in which the inert fusingagent is added in the step (2). In the case of adding the inert fusingagent in the step (3), the amount of the inert fusing agent becomeseasily controlled by means of washing the co-precipitate obtained in thestep (2), and reducing the amount of the alkali remaining in theco-precipitate or a negative ion derived from a salt of Ni, a salt ofMn, or a salt of Co.

The inert fusing agent may remain in the lithium composite metal oxide,or may be removed by washing.

The content of the inert fusing agent in the mixture during the heatingmay be appropriately determined, and, as the content of the inert fusingagent increases, the average particle diameter tends to decrease. Inorder to make the particle diameters of the lithium composite metaloxide more uniform, the content of the inert fusing agent is preferably0.1 parts by mass or more, and more preferably 1 part by mass or morewith respect to 100 parts by mass of the lithium compound in themixture. To increase the reaction activity between the lithium compoundand the co-precipitate, the content of the inert fusing agent ispreferably 400 parts by mass or less, and more preferably 100 parts bymass or less with respect to 100 parts by mass of the lithium compoundin the mixture. The above-described upper limit value and lower limitvalue may be adequately selected.

The lithium composite metal oxide obtained after the heating may beground using a ball mill, a jet mill, etc. The BET specific surface areaand average particle diameter of the lithium composite metal oxide canbe occasionally controlled by grinding. In addition, heating may becarried out after the grinding by means of grinding the lithiumcomposite metal oxide obtained by carrying out the steps (1) to (3)followed by carrying out the step (3) again. Furthermore, the grindingand the heating in the step (3) may be repeated two or more times asnecessary. In addition, the lithium composite metal oxide may also bewashed and classified as necessary.

The above-described method is a method for producing the lithiumcomposite metal oxide including M. In the above-described method, when Mis not used, the lithium composite metal oxide including no M isobtained.

The lithium composite metal oxide of the present embodiment obtained inthe above-described manner becomes a mixture of, typically, primaryparticles and secondary particles formed by the agglomeration of theprimary particles.

When the lithium composite metal oxide is used as a positive electrodeactive material for a non-aqueous electrolyte secondary battery, anon-aqueous electrolyte secondary battery exhibiting a high dischargecapacity and a high initial coulomb efficiency is obtained.

(Positive Electrode Active Material)

The lithium composite metal oxide of the present embodiment is useful asa positive electrode active material for a non-aqueous electrolytesecondary battery exhibiting a high discharge capacity and a highinitial coulomb efficiency. The positive electrode active material ofthe present embodiment includes the above-described lithium compositemetal oxide of the present embodiment.

In the positive electrode active material of the present embodiment, aslong as the effects of the present invention are not significantlydeteriorated, a compound different from the lithium composite metaloxide may be attached to the surfaces of particles constituting thelithium composite metal oxide.

An example of the compound is a compound containing one or more elementsselected from the group consisting of B, Al, Ga, In, Si, Ge, Sn, Mg, andtransition metal elements, preferably a compound containing one or moreelements selected from the group consisting of B, Al, Mg, Ga, In, andSn, and more preferably a compound of Al. Examples thereof includeoxides, hydroxides, oxyhydroxides, carbonates, nitrates, and organicacid salts of the above-described elements, and preferable examplesthereof include oxides, hydroxides, and oxyhydroxides. In addition, thecompound may be used in a mixture. Among the above-described compounds,alumina is a particularly preferable compound.

After the compound is attached to the surfaces of the particlesconstituting the lithium composite metal oxide, heating may be carriedout.

Since the above-described lithium composite metal oxide of the presentembodiment is used as the above-described positive electrode activematerial, a non-aqueous electrolyte secondary battery using the positiveelectrode active material is capable of exhibiting a higher dischargecapacity and a higher initial coulomb efficiency than ever.

[Non-Aqueous Electrolyte Secondary Battery]

Next, a positive electrode using the positive electrode active materialof the present embodiment, and a non-aqueous electrolyte secondarybattery including the positive electrode will be described withdescribing the constitution of the non-aqueous electrolyte secondarybattery.

An example of the non-aqueous electrolyte secondary battery of thepresent embodiment includes a positive electrode, a negative electrode,a separator disposed between the positive electrode and the negativeelectrode, and an electrolytic solution.

FIG. 1 is a schematic view illustrating an example of the non-aqueouselectrolyte secondary battery of the present embodiment. A cylindricalnon-aqueous electrolyte secondary battery 10 of the present embodimentis formed as described below.

First, as illustrated in FIG. 1(a), two separators 1 having a bandshape, a band-shaped positive electrode 2 having a positive electrodelead 21 at one end, and a band-shaped negative electrode 3 having anegative electrode lead 31 at one end are laminated in an order of theseparator 1, the positive electrode 2, the separator 1, and the negativeelectrode 3, and are coiled, resulting in forming an electrode group 4.

Next, as illustrated in FIG. 1(b), the electrode group 4 and aninsulator, which is not illustrated, are stored in a battery can 5,then, the bottom of the can is sealed, an electrolyte solution 6 isimpregnated into the electrode group 4, and an electrolyte is disposedbetween the positive electrode 2 and the negative electrode 3.Furthermore, the top section of the battery can 5 is sealed using a topinsulator 7 and a sealing body 8, whereby the non-aqueous electrolytesecondary battery 10 can be formed.

The shape of the electrode group 4 can be, for example, a columnar shapeof which the cross-sectional shape becomes round, oval, a rectangularshape, or a rectangular shape with rounded edges when the electrodegroup 4 is cut in a direction perpendicular to the coiling axis.

As the shape of the non-aqueous electrolyte secondary battery includingthe above-described electrode group 4, it is possible to employ theshapes determined by IEC60086, which is the standard of batteriesdetermined by the International Electrotechnical Commission (IEC), orJIS C 8500. Examples thereof include a cylindrical shape, an angularshape, etc.

The non-aqueous electrolyte secondary battery is not limited to theabove-described coiled constitution, and may have a laminatedconstitution obtained by laminating a positive electrode, a separator, anegative electrode, and a separator repeatedly. Examples of thelaminated non-aqueous electrolyte secondary battery include a so-calledcoin-type battery, a button-type battery, and a paper-type (orsheet-type) battery.

Hereinafter, the respective constitutions will be sequentiallydescribed.

(Positive Electrode)

The positive electrode of the present embodiment can be manufactured by,first, preparing a positive electrode mixture including theabove-described positive electrode active material of the presentembodiment, a conductive material, and a binder, and supporting thepositive electrode mixture by a positive electrode current collector.

(Conductive Material)

As the conductive material included in the positive electrode of thepresent embodiment, a carbon material can be used. Examples of thecarbon material include graphite powder, carbon black (for example,acetylene black), fibrous carbon materials, etc. Since the carbon blackis a micro particle and has a great surface area, the conductivity inthe positive electrode can be increased, and the charge and dischargeefficiency and the output characteristics can be improved by adding asmall amount of the carbon black to the positive electrode mixture;however, when the carbon black is excessively added, both the bindingstrength between the positive electrode mixture and the positiveelectrode current collector by the binder and the binding strengthinside the positive electrode mixture decrease, and conversely, theinternal resistance is increased.

The proportion of the conductive material in the positive electrodemixture is preferably from 5 parts by mass to 20 parts by mass withrespect to 100 parts by mass of the positive electrode active material.In the case of using a fibrous carbon material such as a graphitizedcarbon fiber or a carbon nanotube as the conductive material, it is alsopossible to decrease the proportion.

(Binder)

As the binder included in the positive electrode of the presentembodiment, a thermoplastic resin can be used.

Examples of the thermoplastic resin include fluorine resins such aspolyvinylidene fluoride (hereinafter, in some cases, referred to asPVdF), polytetrafluoroethylene (hereinafter, in some cases, referred toas PTFE), ethylene tetrafluoride·propylene hexafluoride·vinylidenefluoride-based copolymers, propylene hexafluoride·vinylidenefluoride-based copolymers, and ethylene tetrafluoride·perfluorovinylether-based copolymers; polyolefin resins such as polyethylene andpolypropylene.

Two or more thermoplastic resins may be used in a mixture thereof. Whena fluorine resin and a polyolefin resin are used as the binder, by meansof adjusting the proportion of the fluorine resin of from 1 mass % to 10mass %, and the proportion of the polyolefin resin of from 0.1 mass % to2 mass % in the entire positive electrode mixture, it is possible toobtain a positive electrode mixture having a strong adhesive force tothe positive electrode current collector.

(Positive Electrode Current Collector)

As the positive electrode current collector included in the positiveelectrode of the present embodiment, it is possible to use a band-shapedmember constituted of a metal material such as Al, Ni, or stainlesssteel as a constitutional material. Among the above-described members,in the view point that Al is easy to process and is inexpensive, amember for which Al is used as a forming material and which is formedinto a thin film shape is preferable.

Examples of a method for supporting the positive electrode mixture bythe positive electrode current collector include a method in which thepositive electrode mixture is molded on the positive electrode currentcollector by pressure. The positive electrode mixture can be supportedby the positive electrode current collector by producing paste from thepositive electrode mixture using an organic solvent, applying theobtained paste of the positive electrode mixture to at least one surfaceof the positive electrode current collector, drying the paste, andaffixing the paste through pressing.

In the case of producing the paste from the positive electrode mixture,examples of the organic solvent that can be used include amine-basedsolvents such as N,N-dimethylaminopropyleamine and diethylene triamine;ether-based solvents such as tetrahydrofuran; ketone-based solvents suchas methyl ethyl ketone; ester-based solvents such as methyl acetate; andamide-based solvents such as dimethyl acetamide, N-methyl-2-pyrrolidone(hereinafter, in some cases, referred to as NMP).

Examples of the method for applying the paste of the positive electrodemixture to the positive electrode current collector include a slit diecoating method, a screen coating method, a curtain coating method, aknife coating method, a gravure coating method, and an electrostaticspray method.

The positive electrode can be formed using the above-described method.

(Negative Electrode)

The negative electrode included in the non-aqueous electrolyte secondarybattery of the present embodiment needs to capable of doping andde-doping a lithium ion at a potential lower than that in the positiveelectrode, and examples thereof include an electrode produced bysupporting a negative electrode mixture including a negative electrodeactive material on a negative electrode current collector, and anelectrode constituted of a negative electrode active material only.

(Negative Electrode Active Material)

Examples of the negative electrode active material included in thenegative electrode include materials which are carbon materials,chalcogen compounds (oxides, sulfides, etc.), nitrides, metals, oralloys, and allow a lithium ion to be doped or de-doped at a potentiallower than in the positive electrode.

Examples of the carbon materials that can be used as the negativeelectrode active material include graphite such as natural graphite andartificial graphite, cokes, carbon black, pyrolytic carbons, carbonfibers, and organic macromolecular compound-sintered bodies.

Examples of oxides that can be used as the negative electrode activematerial include oxides of silicon expressed by Formula SiO_(x) (here, xrepresents a positive real number) such as SiO₂ and SiO; oxides oftitanium expressed by Formula TiO_(x) (here, x represents a positivereal number) such as TiO₂ and TiO; oxides of vanadium expressed byFormula VO_(x) (here, x represents a positive real number) such as V₂O₅and VO₂; oxides of iron expressed by Formula FeO_(x) (here, x representsa positive real number) such as Fe₃O₄, Fe₂O₃, and FeO; oxides of tinexpressed by Formula SnO_(x) (here, x represents a positive real number)such as SnO₂ and SnO; oxides of tungsten expressed by General FormulaWO_(x) (here, x represents a positive real number) such as WO₃ and WO₂;and composite metal oxides containing lithium and titanium or vanadiumsuch as Li₄Ti₅O₁₂ and LiVO₂.

Examples of sulfides that can be used as the negative electrode activematerial include sulfides of titanium expressed by Formula TiS_(x)(here, x represents a positive real number) such as Ti₂S₃, TiS₂, andTiS; sulfides of vanadium expressed by Formula VS_(x) (here, xrepresents a positive real number) such as V₃S₄, VS₂, and VS; sulfidesof iron expressed by Formula FeS_(x) (here, x represents a positive realnumber) such as Fe₃S₄, FeS₂, and FeS; sulfides of molybdenum expressedby Formula MoS_(x) (here, x represents a positive real number) such asMo₂S₃, and MoS₂; sulfides of tin expressed by Formula SnS_(x) (here, xrepresents a positive real number) such as SnS₂ and SnS; sulfides oftungsten expressed by Formula WS_(x) (here, x represents a positive realnumber) such as WS₂; sulfides of antimony expressed by Formula SbS_(x)(here, x represents a positive real number) such as Sb₂S₃; and sulfidesof selenium expressed by Formula SeS_(x) (here, x represents a positivereal number) such as Se₅S₃, SeS₂, and SeS.

Examples of nitrides that can be used as the negative electrode activematerial include lithium-containing nitrides such as Li₃N andLi_(3-x)A_(x)N (here, A is either or both Ni and Co, and 0<x<3).

The carbon materials, the oxides, the sulfides, and nitrides may besingly used, or two or more thereof may be jointly used. In addition,the carbon materials, the oxides, the sulfides, and nitrides may becrystalline or amorphous. The carbon materials, the oxides, thesulfides, and nitrides are used as an electrode by being supportedmainly on a negative electrode current collector.

Examples of metals that can be used as the negative electrode activematerial include lithium metals, silicon metals, tin metals, etc.

Examples of alloys that can be used as the negative electrode activematerial include lithium alloys such as Li—Al, Li—Ni, Li—Si, Li—Sn, andLi—Sn—Ni; silicon alloys such as Si—Zn; tin alloys such as Sn—Mn, Sn—Co,Sn—Ni, Sn—Cu, and Sn—La; and alloys such as Cu₂Sb and La₃Ni₂Sn₇.

The metals or alloys are processed into, for example, a foil shape, andthen are mainly used singly as an electrode.

Among the above-described negative electrode materials, since thepotential of the negative electrode rarely changes during charging froma uncharged state to a fully charged state (the potential flatness isfavorable), the average discharge potential is lower, and when thebattery is repeatedly charged and discharged, the capacity maintenancerate is higher (the cycle characteristics are favorable), carbonmaterials including graphite such as natural graphite or artificialgraphite as a main component are preferably used. Examples of the shapeof the carbon material include a flake shape such as natural graphite, aspherical shape such as mesocarbon microbeads, a fibrous shape such as agraphitized carbon fiber, an agglomerate of fine powder, etc., and thecarbon material may have any shape.

The negative electrode mixture may include a binder as necessary. As thebinder, a thermoplastic resin can be used, and examples thereof includePVdF, thermoplastic polyimides, carboxymethyl cellulose, polyethylene,and polypropylene.

(Negative Electrode Current Collector)

Examples of the negative electrode current collector included in thenegative electrode include a band-shaped member constituted of a metalmaterial such as Cu, Ni, or stainless steel as a constitutionalmaterial. Among the above-described members, a member for which Cu isused as a forming material and which is processed into a thin film shapeis preferable since Cu does not easily form an alloy with lithium, andis easily processed.

Examples of the method for supporting the negative electrode mixture onthe above-described negative electrode current collector include,similarly to the case of the positive electrode, a method in which thenegative electrode mixture is supported on the negative electrodecurrent collector through pressurization-molding, and a method in whichpaste is produced using a solvent etc., is applied to and dried on thenegative electrode current collector, and is affixed through pressing.

(Separator)

As the separator included in the non-aqueous electrolyte secondarybattery of the present embodiment, it is possible to use, for example, amaterial which is made of a polyolefin resin such as polyethylene orpolypropylene, a fluorine resin, a nitrogen-containing aromatic polymer,etc., and has a form of a porous film, a non-woven fabric, a wovenfabric, etc. In addition, the separator may be formed using two or morematerials, or may be formed by laminating these materials.

The thickness of the separator is preferably thin as long as themechanical strength is maintained since the volume energy density of thebattery increases, and the internal resistance decreases, and ispreferably approximately from 5 μm to 200 μm, and more preferablyapproximately from 5 μm to 40 μm.

The separator preferably includes a porous film containing athermoplastic resin. The non-aqueous electrolyte secondary batterypreferably has a function of, when an abnormal current flows in abattery due to the short circuit etc. between the positive electrode andthe negative electrode, shielding the current at the short circuitposition to inhibit (shut down) the flow of an excessive current. Theshut-down is performed by softening or melting the porous film in theseparator to shield micro pores, when the separator at the short circuitposition is overheated due to short circuit, and exceeds thepreviously-estimated operational temperature. In addition, even when thetemperature inside the battery increases up to a certain hightemperature after the shut-down, the separator preferably maintains theshut-down state without being broken due to the temperature.

When a porous film is used as the separator, the thermoplastic resinused for the porous film needs to be not dissolved in the electrolyticsolution in the non-aqueous electrolyte secondary battery. Examplesthereof include polyolefin resins such as polyethylene or polypropylene,and thermoplastic polyurethane resins, and a mixture of two or morethermoplastic resins may be used.

In the case of using a porous film as the separator, in order to makethe separator be softened and be shut down at a lower temperature, theporous film preferably contains polyethylene. Examples of thepolyethylene include polyethylene such as low-density polyethylene,high-density polyethylene, and linear polyethylene, and also includeultrahigh-molecular-weight polyethylene having a molecular weight of amillion or more.

To further increase the piercing strength of the porous film used as theseparator, the thermoplastic resin constituting the porous filmpreferably contains at least ultrahigh-molecular-weight polyethylene. Inaddition, there is also a case in which, on the manufacturing surface ofthe porous film, the thermoplastic resin preferably contains a wax madeof polyolefin having a low molecular weight (a weight-average molecularweight of 10000 or less).

In the present embodiment, since the separator favorably transmits anelectrolyte while the battery is in use (is charged and discharged), theair permeability resistance by the Gurley method determined by JIS P8117 is preferably from 50 seconds/100 cc to 300 seconds/100 cc, andmore preferably from 50 seconds/100 cc to 200 seconds/100 cc.

In addition, the porosity of the separator is preferably from 30 vol %to 80 vol %, and more preferably from 40 vol % to 70 vol %. Separatorshaving different porosities may be laminated.

(Electrolyte Solution)

The electrolyte solution included in the non-aqueous electrolytesecondary battery of the present embodiment includes an electrolyte andan organic solvent.

Examples of the electrolyte included in the electrolyte solution includelithium salts such as LiClO₄, LiPF₆, LiAsF₆, LiSbF₆, LiBF₄, LiCF₃SO₃,LiN (SO₂CF₃)₂, LiN (SO₂C₂F₅)₂, LiN (SO₂CF₃) (COCF₃), Li (C₄F₉SO₃), LiC(SO₂CF₃)₃, Li₂B₁₀Cl₁₀, LiBOB (here, BOB represents bis(oxalato)borate),lower aliphatic carboxylic acid lithium salt, and LiAlCl₄. Theabove-described electrolytes may be singly used, or two or moreelectrolytes may be used in a mixture form. Among the above-describedelectrolytes, it is preferable to use an electrolyte including at leastone selected from the group consisting of LiPF₆, LiAsF₆, LiSbF₆, LiBF₄,LiCF₃SO₃, LiN(SO₂CF₃)₂, and LiC(SO₂CF₃)₃ which contain fluorine as theelectrolyte.

In addition, as the organic solvent included in the electrolyte, it ispossible to use, for example, a carbonate such as propylene carbonate,ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methylcarbonate, 4-trifluoromethyl-1,3-dioxolane-2-one, and1,2-di(methoxycarbonyloxy)ethane; an ether such as 1,2-dimethoxyethane,1,3-dimethoxypropane, pentafluoropropyl methyl ether,2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, and2-methyl tetrahydrofuran; an ester such as methyl formate, methylacetate, and γ-butyrolactone; a nitrile such as acetonitrile andbutyronitrile; an amide such as N,N-dimethyl formamide andN,N-dimethylacetoamide; a carbamate such as 3-methyl-2-oxazolidone; asulfur-containing compound such as sulfolane, dimethyl sulfoxide, and1,3-propane sultone; or a solvent produced by further introducing afluoro group into the above-described organic solvent (a solvent inwhich one or more hydrogen atoms included in the organic solvent issubstituted by a fluorine atom).

As the organic solvent, it is preferable to use two or more organicsolvents in a mixture form. Among the above-described organic solvents,a solvent mixture including a carbonate is preferable, and a solventmixture of a cyclic carbonate and a non-cyclic carbonate and a solventmixture of a cyclic carbonate and ether are more preferable. As thesolvent mixture of a cyclic carbonate and a non-cyclic carbonate, asolvent mixture including ethylene carbonate, dimethyl carbonate, andethyl methyl carbonate is preferable. An electrolyte solution using theabove-described solvent mixture has advantages of a wider operationaltemperature range, is more hardly deteriorated when used at a highvoltage, is more hardly deteriorated when used for a long period oftime, and has advantages of being hardly decomposed in the case of usinga graphite material such as natural graphite or artificial graphite asthe active material for the negative electrode.

In addition, in order to improve the stability of the obtainednon-aqueous electrolyte secondary battery, it is preferable to use anelectrolyte solution including a lithium salt containing fluorine suchas LiPF₆ and an organic solvent having a fluorine substituent as theelectrolyte solution. A solvent mixture including ether having afluorine substituent such as pentafluoropropylene methyl ether or2,2,3,3-tetrafluoropropyl difluoromethyl ether and dimethyl carbonate ismore preferable since the capacity maintenance rate is higher even whenthe battery is discharged at a high voltage.

A solid electrolyte may be used instead of the above-describedelectrolytic solution. As the solid electrolyte, it is possible to use,for example, an organic macromolecular electrolyte such as apolyethylene oxide-based macromolecular compound or a macromolecularcompound including at least one polyorganosiloxane chain orpolyoxyalkylene chain. In addition, it is also possible to use aso-called gel-type electrolyte including a non-aqueous electrolyticsolution held in a macromolecular compound. In addition, it is alsopossible to use an inorganic solid electrolyte including a sulfide suchas Li₂S-SiS₂, Li₂S-GeS₂, Li₂S-P₂S₅, Li₂S-B₂S₃, Li₂S-SiS₂-Li₃PO₄, orLi₂S-SiS₂-Li₂SO₄. The use of the solid electrolyte is occasionallycapable of improving the stability of the non-aqueous electrolytesecondary battery.

In the non-aqueous electrolyte secondary battery of the presentembodiment, when the solid electrolyte is used, the solid electrolyteplays a role of the separator, and, in such a case, the separator maynot be required.

Among non-aqueous electrolyte secondary batteries for which the positiveelectrode active material including the lithium composite metal oxide ofthe present embodiment is used, there is a non-aqueous electrolytesecondary battery in which the charge potential of the positiveelectrode at a fully charged state reaches 4.35 V (vs. Li/Li⁺) or more.This non-aqueous electrolyte secondary battery exhibits a high dischargecapacity, and this is preferable. Here, the “charge potential of thepositive electrode at a fully charged state being 4.35 V (vs. Li/Li⁺) ormore” means that the charge potential of the positive electrode is 4.35V or more when a non-aqueous electrolyte secondary battery (testbattery) produced using the positive electrode and metal lithium as anegative electrode is fully charged.

Since the above-described positive electrode includes the positiveelectrode active material for which the above-described lithiumcomposite metal oxide of the present embodiment is used, the non-aqueouselectrolyte secondary battery is capable of exhibiting a higherdischarge capacity and a higher initial coulomb efficiency than ever.Since the above-described non-aqueous electrolyte secondary batteryincludes the above-described positive electrode, the non-aqueouselectrolyte secondary battery exhibits a higher discharge capacity and ahigher initial coulomb efficiency than before.

EXAMPLES

Next, the present invention will be described in more detail usingexamples.

In the present example, the evaluation of lithium composite metal oxides(positive electrode active materials) and the production and evaluationof positive electrodes and lithium secondary batteries were carried outas described below.

(1) Evaluation of the Lithium Composite Metal Oxide

1. Analysis of the Composition of the Lithium Composite Metal Oxide

The composition of the lithium composite metal oxide was analyzed usingan inductively-coupled plasma emission analyzer (SPS3000 manufactured bySII Nano Technology) after the powder of the obtained lithium compositemetal oxide was dissolved in hydrochloric acid.

2. Measurement of the BET Specific Surface Area of the Lithium CompositeMetal Oxide

The BET specific surface area of the lithium composite metal oxide wasmeasured using a FLOWSORB II2300 manufactured by MicromeriticsInstrument Corporation after 1 g of lithium composite metal oxide powderwas dried at 150° C. in a nitrogen atmosphere for 15 minutes.

3. Measurement of the Average Particle Diameter of the Lithium CompositeMetal Oxide

0.1 g of lithium composite metal oxide powder to be measured was putinto 50 ml of a 0.2 mass % sodium hexametaphosphate aqueous solution,and a dispersion liquid in which the powder was dispersed was obtained.The particle size distribution of the obtained dispersion liquid wasmeasured using a MASTERSIZER 2000 (a laser diffraction scatteringparticle size distribution measuring instrument) manufactured by MalvernInstruments Ltd., and a volume-based cumulative particle sizedistribution curve was obtained. In the obtained cumulative particlesize distribution curve, the value of the particle diameter (D₅₀) fromthe micro particle side at the time of 50% accumulation was used as theaverage particle diameter of the lithium composite metal oxide.

4. Measurement of the Average Primary Particle Diameter of the LithiumComposite Metal Oxide

The lithium composite metal oxide powder were placed on a conductivesheet attached onto a sample stage, and SEM observation was carried outby radiating an electron beam with an accelerated voltage of 20 kV usinga JSM-5510 manufactured by JEOL Ltd. 50 primary particles werearbitrarily selected from an image (SEM photograph) obtained from theSEM observation, parallel lines were drawn from a certain direction soas to hold a projection image of each primary particle, and the distance(unidirectional particle diameter) between the parallel lines wasmeasured as the particle diameter of the primary particle. Thearithmetic average value of the obtained particle diameters of theprimary particles was used as the average primary particle diameter ofthe lithium composite metal oxide.

5. Powder X-Ray Diffraction Measurement of the Lithium Composite MetalOxide

The powder X-ray diffraction of the lithium composite metal oxide wasmeasured using a powder X-ray diffraction apparatus (RINT2500TTRmanufactured by Rigaku Corporation, horizontal specimen type). Theobtained lithium composite metal oxide was loaded into a dedicatedsubstrate, and the measurement was carried out in a range of diffractionangle 2θ=10° to 90° using a Cu-Kα radiation source, thereby obtaining apowder X-ray diffraction pattern.

In addition, the Rietveld analysis of the powder X-ray diffractionpattern was carried out using an analysis program RIETAN-2000 (refer toF. Izumi and T. Ikeda, Mater. Sci. Forum. 321-324 (2000) 198), and aspace group of the crystal structure of the lithium composite metaloxide was obtained.

(2) Production of a Positive Electrode

A lithium composite metal oxide (positive electrode active material)obtained using a production method described below, a conductivematerial (including acetylene black and graphite at a mass ratio of9:1), and a binder (PVdF) were added and kneaded so as to obtain acomposition of the positive electrode active material, the conductivematerial, and the binder at a mass ratio of 87:10:3, thereby preparing apaste-form positive electrode mixture. During the preparation of thepositive electrode mixture, N-methyl-2-pyrrolidone was used as anorganic solvent.

The obtained positive electrode mixture was applied to a 40 μm-thick Alfoil which served as a current collector, and was dried in a vacuum at150° C. for eight hours, thereby obtaining a positive electrode.

(3) Production of a Non-Aqueous Electrolyte Secondary Battery (CoinCell)

The following operations were carried out in a glove box in an argonatmosphere.

The positive electrode produced in the “(2) production of a positiveelectrode” was placed on a bottom lid of a coin cell for a coin-typebattery R2032 (manufactured by Hohsen Corporation) with the aluminumfoil surface facing downward, and a laminate film separator (a separatorincluding a heat-resistant porous layer laminated on a polyethyleneporous film (thickness: 16 μm)) was placed on the positive electrode.300 μl of an electrolytic solution was injected thereinto. Theelectrolyte solution used was prepared by dissolving 1 mol/l of LiPF₆ ina liquid mixture of ethylene carbonate, dimethyl carbonate, and ethylmethyl carbonate at a volume ratio of 30:35:35.

Next, metal lithium used as a negative electrode was placed on thelaminate film separator, was covered with a top lid through a gasket,and was swaged using a swage, thereby producing a non-aqueouselectrolyte secondary battery (coin-type battery R2032, hereinafter, insome cases, referred to as “coin-type battery”).

(4) Charge and Discharge Test

A charge and discharge test was carried out under conditions describedbelow using the coin-type battery produced in the “(3) production of anon-aqueous electrolyte secondary battery (coin cell)”. The chargecapacity, the discharge capacity, and the initial coulomb efficiency inthe charge and discharge test were obtained respectively as describedbelow.

<Charge and Discharge Test>

Test temperature: 25° C.

Charging conditions: maximum charging voltage 4.6 V, charging time 20hours, charging current 0.5 mA/cm²

Discharging conditions: minimum discharging voltage 2.5 V, dischargingtime 20 hours, discharging current 0.5 mA/cm²

Initial coulomb efficiency (o)=initial discharge capacity(mAh/g)/initial charge capacity (mAh/g)×100

Example 1

1. Production of a Precursor (Co-Precipitate) of a Lithium CompositeMetal Oxide

Nickel sulfate hexahydrate and manganese sulfate hydrate were weighedrespectively so that the molar ratio of Ni:Mn reached 0.25:0.75, andwere dissolved in pure water, thereby obtaining a transition metalaqueous solution containing Ni, Mn, and SO₄.

Co-precipitation was carried out by adding a potassium hydroxide aqueoussolution to the transition metal aqueous solution, and a precipitate wasgenerated, thereby obtaining a slurry. Solid-liquid separation wascarried out on the obtained slurry, the slurry was washed usingdistilled water, and was dried at 150° C., thereby obtaining aco-precipitate F¹.

2. Production and Evaluation of a Lithium Composite Metal Oxide

The obtained co-precipitate F¹, lithium carbonate was weighed so thatthe amount (mole) of Li reached 1.5 times the total amount (mole) of Niand Mn contained in the obtained co-precipitate F¹, and potassiumsulfate as an inert fusing agent were mixed using a mortar, therebyobtaining a mixture.

Next, the obtained mixture was put into an alumina calcining container,and the alumina calcining container was put into an electric furnace.The alumina calcining container was held at 850° C. in the atmospherefor six hours, heated, and cooled to room temperature, thereby obtaininga calcined material.

The obtained calcined product was ground, and was dispersed in distilledwater. After supernatants generated after the calcined product was leftto stand were removed by decantation, the calcined product was filtered,and was dried at 300° C. for six hours, thereby obtaining a powder-formlithium composite metal oxide E¹.

As a result of analyzing the composition of the obtained E¹, the molarratio of Li:Ni:Mn contained in E¹ was 1.30:0.27:0.73.

In addition, the BET specific surface area of E¹ was 26.1 m2/g.

In addition, the average particle diameter of E¹ was 2.3 μm, and theaverage primary particle diameter was 0.15 μ.

When a powder X-ray diffraction measurement of E¹ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of E¹ belonged to a space group of C2/m.

3. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using E¹, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 283, the dischargecapacity (mAh/g) was 233, and the initial coulomb efficiency (%) was82.3.

Example 2

1. Production of a Precursor (Co-Precipitate) of a Lithium CompositeMetal Oxide

The same operation as in Example 1 except for the fact that nickelsulfate hexahydrate and manganese sulfate hydrate were weighedrespectively so that the molar ratio of Ni:Mn reached 0.40:0.60 wascarried out, thereby obtaining a co-precipitate F².

2. Production and Evaluation of a Lithium Composite Metal oxide

The same operation as in Example 1 except that lithium carbonate wasweighed so that the amount (mole) of Li reached 1.3 times the totalamount (mole) of Ni and Mn contained in the obtained co-precipitate F²was carried out, thereby obtaining a lithium composite metal oxide E².

As a result of analyzing the composition of the obtained E², the molarratio of Li:Ni:Mn contained in E² was 1.14:0.42:0.58.

In addition, the BET specific surface area of E² was 15.7 m²/g.

In addition, the average particle diameter of E² was 1.7 μm, and theaverage primary particle diameter was 0.18 μm.

When a powder X-ray diffraction measurement of E² was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of E² belonged to a space group of R3-m.

3. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using E², and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 272, the dischargecapacity (mAh/g) was 235, and the initial coulomb efficiency (%) was86.4.

Example 3

1. Production of a Precursor (Co-Precipitate) of a Lithium CompositeMetal Oxide

Nickel sulfate hexahydrate, manganese sulfate hydrate, and cobaltsulfate heptahydrate were weighed respectively so that the molar ratioof Ni:Mn:Co reached 0.23:0.68:0.09, and were dissolved in pure water,thereby obtaining a transition metal aqueous solution containing Ni, Mn,Co, and SO₄.

Co-precipitation was carried out by adding a potassium hydroxide aqueoussolution to the transition metal aqueous solution, and a precipitate wasgenerated, thereby obtaining a slurry. Solid-liquid separation wascarried out on the obtained slurry, the slurry was washed usingdistilled water, and was dried at 150° C., thereby obtaining aco-precipitate F³.

2. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 1 except that lithium carbonate wasweighed so that the amount (mole) of Li reached 1.5 times the totalamount (mole) of Ni, Mn, and Co contained in the obtained co-precipitateF³ was carried out, thereby obtaining a lithium composite metal oxideE³.

As a result of analyzing the composition of the obtained E³, the molarratio of Li:Ni:Mn:Co contained in E³ was 1.29:0.24:0.68:0.08.

In addition, the BET specific surface area of E³ was 21.2 m²/g.

In addition, the average particle diameter of E³ was 3.3 μm, and theaverage primary particle diameter was 0.13 μm.

When a powder X-ray diffraction measurement of E³ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of E³ belonged to a space group of C2/m.

3. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using E³, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 332, the dischargecapacity (mAh/g) was 288, and the initial coulomb efficiency (%) was86.7.

Example 4

1. Production of a Precursor (Co-Precipitate) of a Lithium CompositeMetal Oxide

The same operation as in Example 3 except that nickel sulfatehexahydrate, manganese sulfate hydrate, and cobalt sulfate heptahydratewere weighed respectively so that the molar ratio of Ni:Mn:Co reached0.34:0.53:0.13 was carried out, thereby obtaining a co-precipitate F⁴.

2. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 1 except that lithium carbonate wasweighed so that the amount (mole) of Li reached 1.3 times the totalamount (mole) of Ni, Mn, and Co contained in the obtained co-precipitateF⁴ was carried out, thereby obtaining a lithium composite metal oxideE⁴.

As a result of analyzing the composition of the obtained E⁴, the molarratio of Li:Ni:Mn:Co contained in E⁴ was 1.19:0.34:0.53:0.13.

In addition, the BET specific surface area of E⁴ was 13.4 m²/g.

In addition, the average particle diameter of E⁴ was 2.8 μm, and theaverage primary particle diameter was 0.18 μm.

When a powder X-ray diffraction measurement of E⁴ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of E⁴ belonged to a space group of C2/m.

3. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using E⁴, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 266, the dischargecapacity (mAh/g) was 230, and the initial coulomb efficiency (%) was86.5.

Example 5

1. Production of a Precursor (Co-Precipitate) of a Lithium CompositeMetal Oxide

The same operation as in Example 3 except that nickel sulfatehexahydrate, manganese sulfate hydrate, and cobalt sulfate heptahydratewere weighed respectively so that the molar ratio of Ni:Mn:Co reached0.20:0.65:0.15 was carried out, thereby obtaining a co-precipitate F⁵.

2. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 1 except that lithium carbonate wasweighed so that the amount (mole) of Li reached 1.5 times the totalamount (mole) of Ni, Mn, and Co contained in the obtained co-precipitateF⁵ was carried out, thereby obtaining a lithium composite metal oxideE⁵.

As a result of analyzing the composition of the obtained E⁵, the molarratio of Li:Ni:Mn:Co contained in E⁴ was 1.36:0.20:0.65:0.15.

In addition, the BET specific surface area of E⁵ was 16.3 m²/g.

In addition, the average particle diameter of E⁵ was 2.3 μm, and theaverage primary particle diameter was 0.18 μm.

When a powder X-ray diffraction measurement of E⁵ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of E⁵ belonged to a space group of C2/m.

3. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using E⁵, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 316, the dischargecapacity (mAh/g) was 289, and the initial coulomb efficiency (%) was91.5.

Example 6

1. Production of a Precursor (Co-Precipitate) of a Lithium CompositeMetal Oxide

The same operation as in Example 3 except that nickel sulfatehexahydrate, manganese sulfate hydrate, and cobalt sulfate heptahydratewere weighed respectively so that the molar ratio of Ni:Mn:Co reached0.28:0.48:0.24 was carried out, thereby obtaining a co-precipitate F⁶.

2. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 1 except that lithium carbonate wasweighed so that the amount (mole) of Li reached 1.3 times the totalamount (mole) of Ni, Mn, and Co contained in the obtained co-precipitateF⁶ was carried out, thereby obtaining a lithium composite metal oxideE⁶.

As a result of analyzing the composition of the obtained E⁶, the molarratio of Li:Ni:Mn:Co contained in E⁶ was 1.13:0.28:0.48:0.24.

In addition, the BET specific surface area of E⁶ was 11.2 m²/g.

In addition, the average particle diameter of E⁶ was 0.6 μm, and theaverage primary particle diameter was 0.19 μm.

When a powder X-ray diffraction measurement of E⁶ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of E⁶ belonged to a space group of R-3m.

3. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using E⁶, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 263, the dischargecapacity (mAh/g) was 220, and the initial coulomb efficiency (%) was83.7.

Example 7

1. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 1 except that firing was carried out at900° C. was carried out, thereby obtaining a lithium composite metaloxide E⁷.

As a result of analyzing the composition of the obtained E⁷, the molarratio of Li:Ni:Mn contained in E⁷ was 1.28:0.27:0.73.

In addition, the BET specific surface area of E⁷ was 23.4 m²/g.

In addition, the average particle diameter of E⁷ was 2.8 μm, and theaverage primary particle diameter was 0.13 μm.

When a powder X-ray diffraction measurement of E⁷ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of E⁷ belonged to a space group of C2/m.

2. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using E⁷, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 263, the dischargecapacity (mAh/g) was 222, and the initial coulomb efficiency (%) was84.4.

Example 8

1. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 2 except that calcining was carried outat 900° C. was carried out, thereby obtaining a lithium composite metaloxide E⁸.

As a result of analyzing the composition of the obtained E⁸, the molarratio of Li:Ni:Mn contained in E⁸ was 1.25:0.43:0.57.

In addition, the BET specific surface area of E⁸ was 9.4 m²/g.

In addition, the average particle diameter of E⁸ was 0.7 μm, and theaverage primary particle diameter was 0.19 μm.

When a powder X-ray diffraction measurement of E⁸ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of E⁸ belonged to a space group of C2/m.

2. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using E⁸, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 281, the dischargecapacity (mAh/g) was 235, and the initial coulomb efficiency (%) was83.6.

Example 9

1. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 3 except that calcining was carried outat 900° C. was carried out, thereby obtaining a lithium composite metaloxide E⁹.

As a result of analyzing the composition of the obtained E⁹, the molarratio of Li:Ni:Mn:Co contained in E⁹ was 1.25:0.23:0.68:0.09.

In addition, the BET specific surface area of E⁹ was 13.0 m²/g.

In addition, the average particle diameter of E⁹ was 2.6 μm, and theaverage primary particle diameter was 0.17 μm.

When a powder X-ray diffraction measurement of E⁹, a diffraction peakwas present at 2θ=20.8°. In addition, the crystal structure of E⁹belonged to a space group of C2/m.

2. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using E⁹, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 335, the dischargecapacity (mAh/g) was 283, and the initial coulomb efficiency (%) was84.5.

Example 10

1. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 4 except that calcining was carried outat 900° C. was carried out, thereby obtaining a lithium composite metaloxide E¹⁰.

As a result of analyzing the composition of the obtained E¹⁰, the molarratio of Li:Ni:Mn:Co contained in E¹⁰ was 1.11:0.34:0.53:0.13.

In addition, the BET specific surface area of E¹⁰ was 7.4 m²/g.

In addition, the average particle diameter of E¹⁰ was 0.3 μm, and theaverage primary particle diameter was 0.20 μm.

When a powder X-ray diffraction measurement of E¹⁰ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of E¹⁰ belonged to a space group of R-3m.

2. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using E¹⁰, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 262, the dischargecapacity (mAh/g) was 221, and the initial coulomb efficiency (%) was84.4.

Example 11

1. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 5 except that calcining was carried outat 900° C. was carried out, thereby obtaining a lithium composite metaloxide E¹¹.

As a result of analyzing the composition of the obtained E¹¹, the molarratio of Li:Ni:Mn:Co contained in E¹¹ was 1.28:0.19:0.66:0.15.

In addition, the BET specific surface area of E¹¹ was 11.7 m²/g.

In addition, the average particle diameter of E¹¹ was 2.6 μm, and theaverage primary particle diameter was 0.21 μm.

When a powder X-ray diffraction measurement of E¹¹ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of E¹¹ belonged to a space group of C2/m.

2. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using E¹¹, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 323, the dischargecapacity (mAh/g) was 284, and the initial coulomb efficiency (%) was87.9.

Comparative Example 1

1. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 6 except that calcining was carried outat 900° C. was carried out, thereby obtaining a lithium composite metaloxide C¹.

As a result of analyzing the composition of the obtained C¹, the molarratio of Li:Ni:Mn:Co contained in C¹ was 1.18:0.28:0.47:0.25.

In addition, the BET specific surface area of C¹ was 4.8 m²/g.

In addition, the average particle diameter of C¹ was 1.6 μm, and theaverage primary particle diameter was 0.25 μm.

When a powder X-ray diffraction measurement of C¹ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of C¹ belonged to a space group of R-3m.

2. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using C¹, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 271, the dischargecapacity (mAh/g) was 211, and the initial coulomb efficiency (%) was77.9.

Comparative Example 2

1. Production of a Precursor (Co-Precipitate) of a Lithium CompositeMetal Oxide

The same operation as in Example 3 except that nickel sulfatehexahydrate, manganese sulfate hydrate, and cobalt sulfate heptahydratewere weighed respectively so that the molar ratio of Ni:Mn:Co reached0.05:0.90:0.05 was carried out, thereby obtaining a co-precipitate D².

2. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 1 except for the fact that lithiumcarbonate was weighed so that the amount (mole) of Li reached 1.9 timesthe total amount (mole) of Ni, Mn, and Co contained in the obtainedco-precipitate D² was carried out, thereby obtaining a lithium compositemetal oxide C².

As a result of analyzing the composition of the obtained C², the molarratio of Li:Ni:Mn:Co contained in C² was 1.78:0.05:0.90:0.05.

Inaddition, the BET specific surface area of C² was 5.0 m²/g.

In addition, the average particle diameter of C² was 0.2 μm, and theaverage primary particle diameter was 0.12 μm.

When a powder X-ray diffraction measurement of C² was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of C² belonged to a space group of C2/m.

3. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using C², and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 245, the dischargecapacity (mAh/g) was 140, and the initial coulomb efficiency (%) was57.1.

Comparative Example 3

1. Production of a Precursor (Co-Precipitate) of a Lithium CompositeMetal Oxide

The same operation as in Example 3 except that nickel sulfatehexahydrate, manganese sulfate hydrate, and cobalt sulfate heptahydratewere weighed respectively so that the molar ratio of Ni:Mn:Co reached0.10:0.80:0.10 was carried out, thereby obtaining a co-precipitate D³.

2. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 1 except for the fact that lithiumcarbonate was weighed so that the amount (mole) of Li reached 1.8 timesthe total amount (mole) of Ni, Mn, and Co contained in the obtainedco-precipitate D³ was carried out, thereby obtaining a lithium compositemetal oxide C³.

As a result of analyzing the composition of the obtained C³, the molarratio of Li:Ni:Mn:Co contained in C² was 1.76:0.09:0.82:0.09.

In addition, the BET specific surface area of C³ was 5.1 m²/g.

In addition, the average particle diameter of C³ was 1.0 μm, and theaverage primary particle diameter was 0.15 μm.

When a powder X-ray diffraction measurement of C³ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of C³ belonged to a space group of C2/m.

3. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using C³, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 343, the dischargecapacity (mAh/g) was 200, and the initial coulomb efficiency (%) was58.3.

Comparative Example 4

1. Production of a Precursor (Co-precipitate) of a Lithium CompositeMetal Oxide

The same operation as in Example 3 except that nickel sulfatehexahydrate, manganese sulfate hydrate, and cobalt sulfate heptahydratewere weighed respectively so that the molar ratio of Ni:Mn:Co reached0.13:0.74:0.13 was carried out, thereby obtaining a co-precipitate D⁴.

2. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 1 except that lithium carbonate wasweighed so that the amount (mole) of Li reached 1.7 times the totalamount (mole) of Ni, Mn, and Co contained in the obtained co-precipitateD⁴ was carried out, thereby obtaining a lithium composite metal oxideC⁴.

As a result of analyzing the composition of the obtained C⁴, the molarratio of Li:Ni:Mn:Co contained in C⁴ was 1.60:0.13:0.74:0.13.

In addition, the BET specific surface area of C⁴ was 4.8 m²/g.

In addition, the average particle diameter of C⁴ was 0.2 μm, and theaverage primary particle diameter was 0.19 μm.

When a powder X-ray diffraction measurement of C⁴, a diffraction peakwas present at 2θ=20.8°. In addition, the crystal structure of C⁴belonged to a space group of C2/m.

3. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using C², and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 357, the dischargecapacity (mAh/g) was 242, and the initial coulomb efficiency (%) was67.8.

Comparative Example 5

1. Production and Evaluation of a Lithium Composite Metal Oxide

The same operation as in Example 1 except that lithium carbonate wasweighed so that the amount (mole) of Li reached 2.0 times the totalamount (mole) of Ni and Mn contained in the obtained co-precipitate F²and firing was carried out at 800° C. was carried out, thereby obtaininga lithium composite metal oxide C⁵.

As a result of analyzing the composition of the obtained C⁵, the molarratio of Li:Ni:Mn contained in C⁵ was 1.40:0.41:0.59.

In addition, the BET specific surface area of C⁵ was 33.2 m²/g.

In addition, the average particle diameter of C⁵ was 0.2 μm, and theaverage primary particle diameter was 0.12 μm.

When a powder X-ray diffraction measurement of C⁵ was carried out, adiffraction peak was present at 2θ=20.8°. In addition, the crystalstructure of C⁵ belonged to a space group of C2/m.

3. The Charge and Discharge Test of a Non-Aqueous Electrolyte SecondaryBattery

A coin-type battery was produced using C⁵, and a charge and dischargetest was carried out. The charge capacity (mAh/g) was 328, the dischargecapacity (mAh/g) was 229, and the initial coulomb efficiency (%) was69.8.

The property values of the lithium composite metal oxides used inExamples 1 to 11 and Comparative Examples 1 to 5 are described in Table1.

In addition, for the non-aqueous electrolyte secondary batteriesproduced in Examples 1 to 11 and Comparative Examples 1 to 5, theresults of the charge and discharge tests are described in Table 2.

Regarding the results of the charge and discharge tests, from theviewpoint of the object of the present invention of obtaining anon-aqueous electrolyte secondary battery exhibiting a high dischargecapacity, non-aqueous electrolyte secondary batteries having a dischargecapacity of 220 mAh/g or more were evaluated to be favorable. Inaddition, from the viewpoint of the object of the present invention ofobtaining a non-aqueous electrolyte secondary battery exhibiting a highinitial coulomb efficiency, non-aqueous electrolyte secondary batterieshaving an initial coulomb efficiency of 80% or more were evaluated to befavorable.

Non-aqueous electrolyte secondary batteries that could be evaluated tobe favorable in terms of both the discharge capacity and the initialcoulomb efficiency as a result of the evaluations were determined to becomprehensively favorable.

In Table 2, “O” indicates favorable characteristics, and “X” indicatepoor characteristics.

TABLE 1 BET Average X-ray specific Average primary Crystal diffractionsurface particle particle Firing Compositional ratio structure peakposition area diameter diameter temperature Li/A Ni/A Mn/A Co/A (spacegroup) (2θ, °) (m²/g) (μm) (μm) (° C.) Example 1 1.30 0.27 0.73 —Lamellar (C2/m) 20.8 26.1 2.3 0.15 850 Example 2 1.14 0.42 0.58 —Lamellar (R3-m) 20.8 15.7 1.7 0.18 850 Example 3 1.29 0.24 0.68 0.08Lamellar (C2/m) 20.8 21.2 3.3 0.13 850 Example 4 1.19 0.34 0.53 0.13Lamellar (C2/m) 20.8 13.4 2.8 0.18 850 Example 5 1.36 0.20 0.65 0.15Lamellar (C2/m) 20.8 16.3 2.3 0.18 850 Example 6 1.13 0.28 0.48 0.24Lamellar (R3-m) 20.8 11.2 0.6 0.19 850 Example 7 1.28 0.27 0.73 —Lamellar (C2/m) 20.8 23.4 2.8 0.13 900 Example 8 1.25 0.43 0.57 —Lamellar (C2/m) 20.8 9.4 0.7 0.19 900 Example 9 1.25 0.23 0.68 0.09Lamellar (C2/m) 20.8 13.0 2.6 0.17 900 Example 10 1.11 0.34 0.53 0.13Lamellar (R3-m) 20.8 7.4 0.3 0.20 900 Example 11 1.28 0.19 0.66 0.15Lamellar (C2/m) 20.8 11.7 2.6 0.21 900 Comparative 1.18 0.28 0.47 0.25Lamellar (R3-m) 20.8 4.8 1.6 0.25 900 Example 1 Comparative 1.78 0.050.91 0.05 Lamellar (C2/m) 20.8 5.0 0.2 0.12 850 Example 2 Comparative1.76 0.09 0.82 0.09 Lamellar (C2/m) 20.8 5.1 1.0 0.15 850 Example 3Comparative 1.60 0.13 0.74 0.13 Lamellar (C2/m) 20.8 4.8 0.2 0.19 850Example 4 Comparative 1.40 0.41 0.59 — Lamellar (C2/m) 20.8 33.2 0.20.12 800 Example 5 * A = Ni + Mn + Co

TABLE 2 Charge Discharge Coulomb capacity capacity efficiencyComprehensive (mAh/g) (mAh/g) Result (%) Result evaluation Example 1 283233 ◯ 82.3 ◯ ◯ Example 2 272 235 ◯ 86.4 ◯ ◯ Example 3 332 288 ◯ 86.7 ◯ ◯Example 4 266 230 ◯ 86.5 ◯ ◯ Example 5 316 289 ◯ 91.5 ◯ ◯ Example 6 263220 ◯ 83.7 ◯ ◯ Example 7 263 222 ◯ 84.4 ◯ ◯ Example 8 281 235 ◯ 83.6 ◯ ◯Example 9 335 283 ◯ 84.5 ◯ ◯ Example 10 262 221 ◯ 84.4 ◯ ◯ Example 11323 284 ◯ 87.9 ◯ ◯ Comparative 271 211 X 77.9 X X Example 1 Comparative245 140 X 57.1 X X Example 2 Comparative 343 200 X 58.3 X X Example 3Comparative 357 242 ◯ 67.8 X X Example 4 Comparative 328 229 ◯ 69.8 X XExample 5

As a result of the measurements, in all the non-aqueous electrolytesecondary batteries for which the lithium composite metal oxidesobtained in Examples 1 to 11 were used as the positive electrode activematerials, a high discharge capacity and a high initial coulombefficiency were exhibited, and high-performance secondary batteriescould be obtained.

On the contrary, in the non-aqueous electrolyte secondary batteries forwhich the lithium composite metal oxides obtained in ComparativeExamples 1 to 3 were used as the positive electrode active materials,the discharge capacity and the initial coulomb efficiency were notsufficient.

In addition, in the non-aqueous electrolyte secondary batteries forwhich the lithium composite metal oxides obtained in ComparativeExamples 4 and 5 were used as the positive electrode active materials,the high initial coulomb efficiency was not sufficient.

The above-described results clarify the usefulness of the presentinvention.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a lithiumcomposite metal oxide used in a non-aqueous electrolyte secondarybattery capable of exhibiting a high discharge capacity and a highinitial coulomb efficiency. In addition, it is possible to provide apositive electrode active material, a positive electrode, and anon-aqueous electrolyte secondary battery for which the above-describedlithium composite metal oxide is used.

1. A lithium composite metal oxide which contains Li, Ni, and Mn, has alamellar structure, has a diffraction peak in a range of 2θ=20.8±1° in apowder X-ray diffraction pattern obtained through powder X-raydiffraction measurement using a Cu-Kα radiation, has a BET specificsurface area of from 6 m²/g to 30 m²/g, and has an average particlediameter measured by a laser diffraction scattering method of from 0.1μm to 10 μm, wherein the lithium composite metal oxide is represen tedby Formula (A) described belowLi_(a)Ni_(1-x-y)Mn_(x)M_(y)O₂   (A) , wherein 1.1≦a≦1.6, 0.4≦x≦0.8,0≦y≦0.25, 0.5≦x+y≦0.8, and M represents one or more elements selectedfrom the group consisting of Co, Fe, Mg, Al, and Ca.
 2. The lithiumcomposite metal oxide according to claim 1, wherein an average primaryparticle diameter of the lithium composite metal oxide is from 0.05 μmto 0.3 μm.
 3. The lithium composite metal oxide according to claim 3,wherein M represents one or more elements selected from the groupconsisting of Co and Fe.
 4. A positive electrode active materialcomprising: the lithium composite metal oxide according to Claim
 1. 5. Apositive electrode comprising: the positive electrode active substanceaccording to claim
 6. 6. A non-aqueous electrolyte secondary batterycomprising: a negative electrode and the positive electrode according toclaim
 7. 7. The non-aqueous electrolyte secondary battery according toclaim 8, wherein a charge potential of the positive electrode in a fullycharged state is 4.35 V (vs. Li/Li⁺) or more.